Current technology for crushing powders, such as powdered compounds for use in the pharmaceutical industry and powdered material in general, offers numerous solutions, some of which are alternative to one another, including powder micronisation systems based on the use of a high-energy gaseous-fluid-jet mill, also called a jet mill.
Said jet mills have a relatively simple construction and structure, normally comprising: a circular grinding or micronisation chamber wherein a series of high-energy jets, generated by a compressed gaseous fluid such as air, cause continuous collisions between the powdered product particles, and consequently their micronisation; a system of feeding and loading the powdered material into the micronisation chamber based on the use of a Venturi tube, also simply called a Venturi, namely a narrowing or throat in a pipe into which a gaseous fluid is conveyed so as to cause a negative pressure that attracts the powdered material; and a selection or classification system, of the static or dynamic type, associated with a central zone of the micronisation chamber and designed to classify the crushed and micronised particles and separate them selectively according to particle size.
The high-energy jets of gaseous fluid are inclined in relation to the radius of the micronisation chamber, with the result that said jets cause a fluid dynamic flow of gaseous fluid in said chamber that draws the particles of powdered material with it and presents two components: a first tangential component that rapidly moves the particles of powdered material in a vortex around the axis of the micronisation chamber, and a second radial component that tends to move the particles from the peripheral zone to the central zone of the micronisation chamber.
In this way, the powdered material or product is subjected, in said fluid dynamic flow in the micronisation chamber, to continual mixing and collisions between its particles.
Moreover, in the flow generated by the high-energy jets of gaseous fluid, the particles are subject to a centrifugal force that also leads to classification, whereby the finer and already micronised particles tend to move towards the central inner part of the micronisation chamber, from which they are evacuated, while the larger ones, not yet micronised, tend to remain in the peripheral outer zone of the micronisation chamber and to rotate around the axis on the periphery, thus undergoing further collisions.
The micronisation process is normally but not solely performed on powdered materials and practically dry powders.
Improvements over the years have led to optimisation of the configuration and geometry of the holes or nozzles through which the high-pressure jets of gaseous fluid are activated and created, both in the micronisation chamber and in the micronised particle classification system, where a dynamic classifier has been introduced in particular, already used in other types of apparatus, which uses a rotary element with peripheral wings that only allows micronised particles of the required size to pass through.
Nevertheless, current micronisation technology, including that based on the use of jet mills, still presents problems and limitations that need to be overcome and solved with further improvements, especially as regards feeding of the powdered material to be micronised to the micronisation chamber of the jet mill.
In particular, the current system of feeding the powdered material to be micronised, typically comprising a Venturi tube, as already stated, presents the following problems and drawbacks.                Noise level of Venturi tube. The presence of a Venturi tube means that the feed system is rather noisy. This noise can only be partly attenuated by suitably closing the feed section.        Abrasion of Venturi tube. The Venturi is subject to abrasion over time, due to the passage of the powder. This abrasion phenomenon is particularly accentuated in the throat area of the Venturi tube, causing a reduction in its efficiency with a variation in the operation of the jet mill.        Blockage of Venturi tube. This phenomenon, also called “blow-back”, is particularly accentuated with fatty, electrostatic or damp powders, and tends to project the powder back through the entrance cone of the Venturi tube, thus preventing correct operation of the jet mill.        Irregularity of the dispensed material to be micronised, i.e. an irregular, imprecise quantity of powdered material, which is fed through the Venturi tube to the jet mill. With the dispensing systems normally used at present, such as single- or double-screw or rotary-valve dispensers, the powder flows into the Venturi tube in an irregular, uncontrolled way, with the result that the quantity of powdered material dispensed by said dispensing systems and the corresponding particle size vary over time, in an uncontrolled way.        Limitation of the ratio obtainable between the quantity of powder dispensed and the operating pressure of the gaseous fluid in the jet mill. As the Venturi feed system communicates directly with the micronisation chamber of the jet mill, its operation is necessarily dependent on the conditions in said chamber, so in order to obtain the negative pressure involved in the Venturi effect, the pressure of the gaseous fluid in the Venturi tube must be at least equal to that of the gaseous fluid in the zone of the nozzles that dispense the high-energy jets for micronisation of the powder. Moreover, for each grinding or micronisation pressure value there is a minimum quantity of powder, dependent on the density, size and other characteristics of the powder which must be fed into the micronisation chamber to allow the operation of the mill and prevent blow-back.        Finally, a further drawback of the current technology which needs to be remedied, again associated with the use of a Venturi type feed system, is that with said Venturi system it is practically impossible to control and feed to the jet mill relatively low flow rates or quantities of the material to be micronised, and at the same time operate with high operating pressures in the jet mill to activate the high-energy fluid jets for micronisation of the powdered material.        
Furthermore, it is remarked that screw feeders, as those adopted in the actual technique, for feeding and transporting powders, have relevant problems related to the metal abrasion during the feeding, that can contaminate the final product.
Moreover screw type feeders cannot inject powders directly into a jet mill.
Indeed, as before discussed, in order to inject the powders an additional tool for acceleration and injection of the powders is required, as for example a Venturi type pneumatic feeder that aspirates the powder leaving the screw and finally blow it with high gas consumption into the spiral mill.
Beneath all mentioned disadvantages and limitations the screw feeder and the Venturi system underlay and imply strong wear if abrasive powders have to be transported.
Still, screw type feeders cannot feed sticky powders or powders with low or no flowing behavior (e.g. flake like powders, short fibres or most of powders with average particle size below 10 microns down to nanometers) and cleaning is very difficult and time consuming.
It is also remarked that the nowadays increasing demand of powders with submicron and nanometre sized particles requires efficient production methods, and the actual state of the art of jet milling technologies appears as not being capable of completely fulfilling this task, as above outlined.
For instance, blocky shape abrasive diamond powders with a particle size below 10 microns cannot be efficiently transported by using a screw type feeder, as those adopted at present in the technique.
Moreover also the methods for producing powders, in particular with low impurities, to be used in application involving grinding or lapping, as diamond powders, SiC (Silicon Carbide), WC (Tungsten Carbide), CBN (Cubic Boron Nitride) and B4C (Boron Carbide) powders, appear to require further improvements.